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From: Stefan Hajnoczi <stefanha@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>,
qemu-devel@nongnu.org
Subject: [PULL for-6.1 2/3] block/io_uring: resubmit when result is -EAGAIN
Date: Thu, 29 Jul 2021 17:22:38 +0100
Message-Id: <20210729162239.932125-3-stefanha@redhat.com>
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Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org,
Stefan Hajnoczi <stefanha@gmail.com>, Julia Suvorova <jusual@redhat.com>,
Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>,
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From: Fabian Ebner <f.ebner@proxmox.com>
Linux SCSI can throw spurious -EAGAIN in some corner cases in its
completion path, which will end up being the result in the completed
io_uring request.
Resubmitting such requests should allow block jobs to complete, even
if such spurious errors are encountered.
Co-authored-by: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
Message-id: 20210729091029.65369-1-f.ebner@proxmox.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
block/io_uring.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/block/io_uring.c b/block/io_uring.c
index 00a3ee9fb8..dfa475cc87 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -165,7 +165,21 @@ static void luring_process_completions(LuringState *s)
total_bytes =3D ret + luringcb->total_read;
=20
if (ret < 0) {
- if (ret =3D=3D -EINTR) {
+ /*
+ * Only writev/readv/fsync requests on regular files or host b=
lock
+ * devices are submitted. Therefore -EAGAIN is not expected bu=
t it's
+ * known to happen sometimes with Linux SCSI. Submit again and=
hope
+ * the request completes successfully.
+ *
+ * For more information, see:
+ * https://lore.kernel.org/io-uring/20210727165811.284510-3-ax=
boe@kernel.dk/T/#u
+ *
+ * If the code is changed to submit other types of requests in=
the
+ * future, then this workaround may need to be extended to dea=
l with
+ * genuine -EAGAIN results that should not be resubmitted
+ * immediately.
+ */
+ if (ret =3D=3D -EINTR || ret =3D=3D -EAGAIN) {
luring_resubmit(s, luringcb);
continue;
}
--=20
2.31.1